The Heart

Question 1

What arteries supply blood to the heart?

Answer 1

There are two main arteries that supply the heart, the right and left coronary arteries that originate from the right and left aortic sinuses on the aorta.

Question 2

What are the branches of the left and right coronary arteries?

Answer 2

The left coronary artery branches off to form the left anterior descending artery, which branches to form the left marginal artery and the left circumflex artery. In 20-25% of individuals, the left circumflex artery contributes to the posterior interventricular artery.
The right coronary artery branches to form the right marginal artery. In 80-85% of individuals, it contributes to the posterior interventricular artery.

Question 3

Where do the coronary arteries run along the heart?

Answer 3

RCA runs along the coronary sulcus before branching. Right marginal artery runs towards the apex. The posterior interventricular artery runs along the posterior interventricular sulcus towards the apex. LCA runs between the left side of the pulmonary trunk and left auricle.The left anterior descending artery follows the anterior interventricular groove towards the apex. The circumflex branch follows the coronary sulcus onto the posterior side. The left marginal artery follows the left border of the heart.

Question 4

What areas of the heart do the different coronary arteries supply?

Answer 4

Right coronary artery - supplies right atrium and right ventricle
Right marginal artery - supplies the right ventricle and the apex
Posterior interventricular artery - supplies the right and left ventricles and interventricular septum

Question 5

What is the drainage system of the heart?

Answer 5

Blood drains from the thebesian veins from the myocardium which drain into the coronary sinus which is found in the posterior coronary sinus. The coronary sinus drains into the right atrium. There are 5 tributaries of the coronary sinus: the great cardiac vein, small cardiac vein, middle cardiac vein, the left marginal vein and the left posterior ventricular vein.

Question 6

What are the auricles?

Answer 6

Right auricle (articular appendage) is a muscular pouch that helps expand the capacity of the right atrium. Present on the antero-medial portion of the right atrium.

Left auricle (articular appendage) has the same function but extends superiorly from the left atrium, overlapping the root of the pulmonary trunk.

Question 7

What is the right atrium?

Answer 7

Receives deoxygenated blood from the inferior and superior vena cava and the coronary veins. It pumps blood through the atrioventricular orifice through the tricuspid valve into the right ventricle. Forms the right border of the heart.

Question 8

What is the left atrium?

Answer 8

Receives oxygenated blood from the 4 pulmonary veins. It pumps blood through the atrioventricular orifice through the mitral valve into the left ventricle. Forms the posterior border of the heart.

Question 9

What is the right ventricle?

Answer 9

Receives deoxygenated blood from the right atrium and pumps it through the pulmonary orifice through the pulmonary valve into the pulmonary artery. Forms the majority of the anterior border of the heart.

Question 10

What is the left ventricle?

Answer 10

Receives oxygenated blood from the left atrium and pumps it through the aortic orifice through the aortic valve into the rest of the body. Form the apex of the heart and the left and diaphragmatic borders.

Question 11

What is the interatrial septum?

Answer 11

Solid muscular wall that separates the right and left atria.

Question 12

What is the interventricular septum?

Answer 12

Separates the 2 ventricles. Made up of a superior membranous part and an inferior muscular part. Muscular part forms the majority of the septum and is the same thickness as the left ventricular wall. The membranous part is thinner and part of the fibrous skeleton of the heart.

Question 13

What is the pathway of blood through the heart?

Answer 13

RIGHT SIDE
Blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart.
As the atrium contracts, blood flows from your right atrium into your right ventricle through the open tricuspid valve.
When the ventricle is full, the tricuspid valve shuts. This prevents blood from flowing backward into the atria while the ventricle contracts.
As the ventricle contracts, blood leaves the heart through the pulmonary valve into the pulmonary artery and to the lungs where it is oxygenated.
LEFT SIDE
The pulmonary veins empty oxygen-rich blood from the lungs into the left atrium of the heart.
As the atrium contracts, blood flows from your left atrium into your left ventricle through the open mitral valve.
When the ventricle is full, the mitral valve shuts. This prevents blood from flowing backward into the atrium while the ventricle contracts.
As the ventricle contracts, oxygen-enriched blood leaves the heart through the aortic valve, into the aorta and to the arteries and eventually into veins to complete the blood circulation in your body.

Question 14

What are the valves of the heart?

Answer 14

Atrioventricular valves: the tricuspid (right) and mitral (left)
Semilunar valves: Pulmonary (right) and Aortic (left)

Question 15

What are the features of the atrioventricular valves?

Answer 15

Atrioventricular valves close at the beginning of ventricular contraction (systole) and produce the first heart sound.
Tricuspid: located between the right atrium and right ventricle. Made up of 3 cusps, base of each cusp is anchored to a fibrous ring.
Mitral: located between the left atrium and the left ventricle. Made up of 2 cusps, base of each cusp is anchored to a fibrous ring.

Question 16

What are the features of the semilunar valves?

Answer 16

Semilunar valves close at the beginning of ventricular relaxation (diastole) and produce the second heart sound.
Pulmonary: located between the right ventricle and the pulmonary trunk. Made up of 3 cusps.
Aortic: located between the left ventricle and the ascending aorta. Made up of 3 cusps.
The sides of each valve leaflet are attached to the walls of the outflow vessel, which is slightly dilated to form a sinus. The free superior edge of each leaflet is thickened (the lunule), and is widest in the midline (the nodule).
At the beginning of ventricular diastole, blood flows back towards the heart, filling the sinuses and pushing the valve cusps together. This closes the valve.

Question 17

What is the pathway of conduction through the heart?

Answer 17

An action potential is created by the Sino-Atrial Node
The wave of excitation spreads across the atria causing them to contract
Upon reaching the Atrioventricular Node the signal is delayed
It is then conducted down the interventricular septum to the Bundle of His
The Bundle of His and the Purkinje fibres spread the wave impulses across the ventricles, causing them to contract

Question 18

What is the SAN?

Answer 18

Collection of pacemaker cells located in the upper wall of the right atrium at the junction where the superior vena cava enters. Generates electrical impulses. The rate at which these are generated depends on the sympathetic nervous system (increasing) and the parasympathetic nervous system (decreasing).

Question 19

What is the AVN?

Answer 19

Present within the atrioventricular septum, near the opening of the coronary sinus. Delays the signal by 120ms to ensure the atria have fully ejected blood into the ventricles. Wave then passes from the AVN to the atrioventricular bundle.

Question 20

What is the Bundle of His?

Answer 20

Transmits impulses from AVN to purkinje fibres. Descends down the membranous part of the interventricular septum before dividing into the right bundle branch (to Purkinje fibres of the right ventricle) and the left bundle branch (to Purkinje fibres of the left ventricle).

Question 21

What are the Purkinje fibres?

Answer 21

Located in the subendocardial surface of the ventricular walls and are able to rapidly transmit cardiac action potentials from the Bundle of His to the myocardium of the ventricles. This rapid conduction allows coordinated ventricular contraction.

Question 22

What is the Crista terminalis?

Answer 22

Vertical ridge of smooth myocardium extending between the superior and inferior vena cava. It provides the origin for pectinate muscles.

Question 23

What are the pectinate muscles?

Answer 23

Parallel ridges in the walls of the atria of the heart.The right atrium has thick and coarse pectinate muscles while these are few smooth and thinner in the left atrium. They act to increase increasing the power of contraction without increasing heart mass substantially.

Question 24

What are the Trabeculae carneae?

Answer 24

Rounded or irregular muscular columns which project from the inner surface of the right and left ventricle of the heart. There are 2 kinds:
Some are attached along their entire length on one side and merely form prominent ridges,
Others are fixed at their extremities but free in the middle, as in the moderator band in the right ventricle, or the papillary muscles
Act to prevent suction that would occur with a flat surfaced membrane and prevent backflow of the blood from the ventricles into the atria.

Question 25

What is the moderator band?

Answer 25

A muscular band of heart tissue found in the right ventricle of the heart. It carries the right branch of the bundle of His and this shortcut across the chamber of the ventricle seems to facilitate conduction time, allowing coordinated contraction of the anterior papillary muscle. Also prevents over-distension of the ventricle.

Question 26

What is the fossa ovalis?

Answer 26

A small oval-shaped depression present in the right atrium.This is the remnant of the foramen ovale in the foetal heart, which allows right to left shunting of blood to bypass the lungs. It closes once the newborn takes its first breath.

Question 27

What does the foetal heart circulation look like?

Answer 27

Blood enters the right atrium and most of it flows through the foramen ovale into the left atrium.
Blood then passes into the left ventricle and then to the aorta
From the aorta, blood is sent to the heart muscle itself and to the brain. After circulating there, the blood returns to the right atrium of the heart through the superior vena cava. About two thirds of the blood will pass through the foramen ovale as described above, but the remaining one third will pass into the right ventricle, toward the lungs.
Most of this blood is bypassed or shunted away from the lungs through the ductus arteriosus to the aorta. Most of the circulation to the lower body is supplied by blood passing through the ductus arteriosus.
This blood then enters the umbilical arteries and flows into the placenta. In the placenta, carbon dioxide and waste products are released into the mother’s circulatory system, and oxygen and nutrients from the mother’s blood are released into the fetus’ blood.

Question 28

What happens if a papillary muscle dies?

Answer 28

A dead papillary muscle will rupture within a few days and will lead to sudden failure of the mitral valve. The blood will not be held in the closed position and blood will leak back into the left atrium during ventricular systole.

Question 29

What is the pathway of the oesophagus?

Answer 29

The oesophagus is a fibromuscular tube that transports food from the pharynx to the stomach. It begins in the neck at the level of C6. Here it is continuous with the laryngopharynx. It descends downward into the superior mediastinum of the thorax between the trachea and the vertebral bodies of T1 to T4. It then enters the abdomen via the oesophageal hiatus at T10. It terminates by joining the cardiac orifice of the stomach at T11.

Question 30

At what phase of the cardiac cycle do the coronary arteries fill? Why?

Answer 30

Blood flows through the coronary arteries during ventricular diastole. Blood flows from high pressure to low pressure. During ventricular systole the highest pressure is in the ventricular lumen and in the myocardium surrounding the lumen. Pressure is lower in the aorta so blood flows out of the ventricle into the aorta. Pressure in the coronary arteries on the surface of the heart is initially lower so these will fill with blood. However, most of the coronary arteries are inside the myocardium where the pressure is highest so these will be squeezed so that they are empty. Blood cannot flow from the surface arteries into the myocardium so there is no flow. During ventricular diastole pressure in the aorta is high, pressure in the myocardium drops to zero; now the coronary arteries inside the muscle can fill and blood flow occurs.

Question 31

What is the blood supply of the sinoatrial node and the atrioventricular node?

Answer 31

The sino-atrial node is supplied by the right coronary artery in 60% of hearts and the left in 40%. The atrioventricular node is supplied by the posterior interventricular artery in all hearts.

Question 32

On a chest X-ray which chambers and vessels form the right and left borders of the cardiac shadow?

Answer 32

Right heart border; right atrium

Left heart border; left auricular appendage superiorly and the left ventricle

Question 33

What is the thoracic duct and where does it join the vascular system?

Answer 33

The thoracic duct is the main lymphatic channel draining lymph from the lower half of the body and the bowel back to the blood stream. The bowel component is important because fat is absorbed into the lymphatics so this is the only route for fat absorption.
It joins the vascular system at the confluence of the left subclavian and left internal jugular vein.

Question 34

What is the azygos system?

Answer 34

The azygos (venous) system is a collective term given to the H-shaped configuration of the azygos, hemiazygos, accessory hemiazygos veins and left superior intercostal vein.
It is responsible for draining the thoracic wall and upper lumbar region via the lumbar veins and posterior intercostal veins. It also provides important collateral circulation between the superior and inferior venae cavae should they become obstructed.

Question 35

What is the azygos vein?

Answer 35

The Azygos enters the thorax via the aortic hiatus in the diaphragm and ascends posteriorly alongside the vertebral bodies, arching over the right main bronchus at T5-T6 and enters the superior vena cava at T4.
The azygos vein receives the lower eight posterior intercostal veins, bronchial veins from the right lung and is joined by the right superior intercostal vein superiorly. Although there is much variability, the azygos vein receives the accessory hemiazygos vein and the hemiazygos vein at the level of T8 and T9 respectively.
The azygos vein contains a valve halfway along the azygos arch (between the vertical azygos vein and the point where the azygos vein enters the SVC). This valve is a common place for the intravenously injected contrast agent to accumulate, which may simulate pathology on CT.

Question 36

What is the accessory hemiazygos vein?

Answer 36

Drains the superior left hemithorax. It arises from the 4th to 8th left posterior intercostal veins and lies longitudinally on the left side of the vertebral bodies. It also drains the left bronchial vein and some veins from the oesophagus. It joins the azygos vein behind the oesophagus at the level of T8.

Question 37

What is the hemiazygos vein?

Answer 37

The hemiazygos vein usually arises from the left ascending lumbar vein and passes through the left crus of the diaphragm. It drains the 9th to 11th left posterior intercostal veins and left subcostal vein, alongside some oesophageal veins. The hemiazygos vein ascends the thorax to the left of the vertebral bodies and passes behind the oesophagus at the level of T9 to join the azygos vein.

Question 38

What is the sympathetic chain?

Answer 38

The sympathetic chain is a component of the autonomic nervous system and is composed of general visceral afferent and efferent axons that allow for involuntary control of bodily functions via the hypothalamus.

Question 39

Where is the sympathetic chain located?

Answer 39

The sympathetic chain is external to the spinal column, adjacent to the vertebral bodies and within the perivertebral space. It is comprised of paired, longitudinally arranged, paravertebral sympathetic ganglia linked together by myelinated axons forming the sympathetic trunk. It extends from the upper neck to the coccyx.
Branches from the prevertebral sympathetic ganglia may communicate with paravertebral sympathetic ganglia and/or form a plexus prior to innervating the target organ.

Question 40

What structures are supplied by the three splanchnic nerves and where does a patient appreciate pain felt by these nerves?

Answer 40

Greater splanchnic nerve; fore gut, felt in the epigastrium.
Lesser splanchnic nerve: midgut, felt round the umbilicus.
Least splanchnic nerve, hind gut, felt around the suprapubic area.

Question 41

What structures drain blood into the azygous system?

Answer 41

The lateral and posterior chest wall and the lateral and posterior abdominal wall.

Question 42

Why is the left recurrent laryngeal nerve at risk from thoracic disease but not the right?

Answer 42

The left recurrent laryngeal nerve passes into the thorax, round the aortic arch and back into the neck. The right recurrent laryngeal does not pass through the thorax.

Question 43

Where do the sympathetic nerves attach to the central nervous system?

Answer 43

The thoracic 1-12 and lumber 1 and 2 spinal segmental nerves.

Question 44

What happens if the sympathetic nerves to the head and neck are damaged?

Answer 44

There will be no sweating on the face (anhidrosis) The eye lid will droop (ptosis) The pupil will be constricted (miosis) Slightly withdrawn eye ball (enopthalmos) This is known as Horner’s syndrome; it almost always effects one side only.